1. Field of the Invention
This invention relates generally to a process and composition for drying gaseous hydrogen halides to remove water impurity therefrom.
2. Description of the Related Art
In numerous industrial and commercial processes, it is desirable to provide gaseous hydrogen halides as high purity, anhydrous materials.
One area in which high purity hydrogen halides are required in essentially completely water-free form is in semiconductor manufacturing operations.
One example, hydrogen chloride is used in semiconductor manufacturing operations for cleaning reactor tubes and susceptors, and as an etchant for the manufacture of microcircuitry devices.
In such applications, highly efficient water vapor removal is required to be carried out on the gaseous hydrogen chloride before its introduction to the end-use environment. Water-containing hydrogen chloride gas is highly corrosive in character, and thus will necessitate frequent replacement of piping, manifolds, valves, etc., with which it comes into contact. In cleaning susceptors, i.e., the support structures on which wafers are processed, the presence of water in the gaseous hydrogen chloride will result in the formation of new oxides on the susceptor, thus opposing the cleaning function which is sought to be carried out. In etching applications, water-containing hydrogen chloride is a source of undesirable moisture contamination in the semiconductor manufacturing environment, which may render the microcircuitry chip products made in such environment deficient or even useless for their intended purpose.
Among the methods which have been utilized by the prior art for removing water from hydrogen chloride is the use of moisture-sorptive molecular sieves. The difficulty of employing such method for production of high-purity hydrogen chloride is that hydrogen chloride is competitive with water for the absorption sites on the molecular sieves. As a result, it is not possible to obtain the necessary lower residual water values, on the order of part per million by volume concentrations and less, in the effluent from the molecular sieve contacting step.
Hydrogen chloride has also been treated with sulfuric acid or phosphoric acid to produce dehydrated hydrogen chloride. Such dehydration methods, however, have the associated disadvantage that they add sulfur or phosphorous to the hydrogen chloride, and these added elements are highly undesirable contaminents in the aforementioned semiconductor manufacturing applications.
Hydrogen bromide is another example of a hydrogen halide which is required in essentially completely water-free condition in the semiconductor manufacturing field. Hydrogen bromide is used in the electronics industry as an etchant for wafers, and as a cleaning agent for susceptors. In these applications, the presence of water impurity in the hydrogen bromide will result in the same disadvantages noted hereinabove in connection with hydrogen chloride in similar applications. In addition, when hydrogen bromide is used as an etchant for wafers, hazing has been found to result when the hydrogen bromide contains even minute amounts of water vapor.
The art has attempted to achieve removal of water from hydrogen bromide by the use of phosphoric acid as a drier. This method, while generally useful to remove the water contaminant, nontheless has the attendant disadvantage that it adds phosphorous to the hydrogen bromide, which as indicated above in connection with hydrogen chloride, is a significant contaminant in the semiconductor manufacturing process.
Similar disadvantages attend the use of other hydrogen halides in these electronics applications.
Japanese Kokai Tokkyo Koho JP 60/222,127 discloses the thermo decomposition of trimethylaluminum to deposit elemental aluminum on a glass substrate, e.g. glass beads, following which the aluminum coating is reacted in arsine to form a scavenger for water and oxygen. Such method is not useful in application to the drying of gaseous hydrogen halides, however, since free arsine would be formed as a reaction product of the scavenger with the hydrogen halide, and would contaminate the dried gas stream.
Accordingly, it is an object of the present invention to provide a highly efficient composition and process for removal of water vapor impurity from gaseous hydrogen halides.
It is a further object of the invention to provide a composition and process of the above type, having a high capacity for water removal, and capable of reducing the water content of the treated hydrogen halide stream to levels on the order of 1 part per million by volume, and less.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.